<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
</head>
<body>
    <script>
        var num = 123;
        function f1() {
            console.log(num); //456
        }

        function f2() {
            console.log(num); //unedfind
            var num = 456;
            f1();
            console.log(num); //456      
        }
        f2();
    </script>
</body>
</html>